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    Re: JPL ephemeresis and Nautical Almanac - speed of light question
    From: John D. Howard
    Date: 2018 Apr 3, 15:15 -0700

    Brad and Frank,

    Yes, I agree with all you both said but if you re-read Rafal's first post he said he wanted to generate a Nautical Almanac for a day.  Yes the JPL data is for solar system bodies - it was established for the US military and NASA and rocket ships and the like ( like the GPS system ).

    My main point was for CelNav we use the apparent position of the sun, stars, and planets ( OK, the Moon too ).  Longitude is based on local apperent solar time.  No need to apply 20 arc seconds per year to a sextant reading that is timed to one second of time (  .25 arc minutes ).  The JPL data is great but not the best source of information when writing a Almanac program.  There are many, simple formula to get the sun's Dec and the EOT and to compute sideral time to the requirements of CelNav.

    My question was more to find out if Rafal's goal was to generate a Nav Almanac or to use JPL data to generate an almanac.  IMHO the JPL route would be a lot of work and over-kill but I agree with you that it can be done.

    John H.

       
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